Embedding Dart in an executable, still possible?

[Jeff Ward]

I've been trying to embed the Dart VM in an executable for a few days and I haven't been having much luck, and I'm wondering if this is still a supported use case.

It would be nice if the following worked:

• Pull the dart source and build libdart
• Link in libdart, include dart_api.h and have that work.

Unfortunately that doesn't work.  But, here's what I've tried and still haven't had much success.

• Pull the dart source and build the full dart executable
• link in libdart, libdart_lib, libdart_vm, libdart_vm_precompiled_runtime, and libdouble_conversion

With this approach, I'm able to build, but when the CreateIsolate callback gets called for the "vm-service" isolate, I call "CreateIsolate" which ASSERTS and exits (the assert is "runtime/vm/hash_table.h:378: error: expected: !data_->IsNull()", where the most relevant function in the callstack is Symbols::AddPredefinedSymbolsToIsolate)

It appears that even though the documentation says Dart_Iniitialize should support supplying a NULL for both the vm_isolate_snapshot and that Dart_CreateIsolate should support supplying a NULL isolate_snapshot, this is no longer the case.

So, I added in the generated snapshot files to my project source (dart_sdk_src\sdk\build\DebugX64\obj\global_intermediate\snapshot_gen.cc) and re-ran. This gets past CreateIsolate, but fails attempting to load the core library. ("Dart_LookupLibrary: library 'dart:builtin' not found.").

I've tried various combinations of compiling in generated files and compiled libs but can't find a combination that links cleanly and supplies a version of dart:builtin.

Obviously there's some amount of secret sauce here I'm missing, but I can't figure out the magic combination to make it work.

--

Jeff

[Florian Schneider]

On Tue, Apr 19, 2016 at 5:13 AM, Jeff Ward <je...@fuzzybinary.com> wrote:

I've been trying to embed the Dart VM in an executable for a few days and I haven't been having much luck, and I'm wondering if this is still a supported use case.

It would be nice if the following worked:

• Pull the dart source and build libdart
• Link in libdart, include dart_api.h and have that work.

Unfortunately that doesn't work.  But, here's what I've tried and still haven't had much success.

• Pull the dart source and build the full dart executable
• link in libdart, libdart_lib, libdart_vm, libdart_vm_precompiled_runtime, and libdouble_conversion

Normally you should only need libdart_vm, and not libdart_vm_precompiled_runtime.

 

With this approach, I'm able to build, but when the CreateIsolate callback gets called for the "vm-service" isolate, I call "CreateIsolate" which ASSERTS and exits (the assert is "runtime/vm/hash_table.h:378: error: expected: !data_->IsNull()", where the most relevant function in the callstack is Symbols::AddPredefinedSymbolsToIsolate)

It appears that even though the documentation says Dart_Iniitialize should support supplying a NULL for both the vm_isolate_snapshot and that Dart_CreateIsolate should support supplying a NULL isolate_snapshot, this is no longer the case.

So, I added in the generated snapshot files to my project source (dart_sdk_src\sdk\build\DebugX64\obj\global_intermediate\snapshot_gen.cc) and re-ran. This gets past CreateIsolate, but fails attempting to load the core library. ("Dart_LookupLibrary: library 'dart:builtin' not found.").

I've tried various combinations of compiling in generated files and compiled libs but can't find a combination that links cleanly and supplies a version of dart:builtin.

Hard to say what exactly is going wrong. Take a close look at runtime/bin/main.cc as an example of how to embed libdart_vm.

 

Obviously there's some amount of secret sauce here I'm missing, but I can't figure out the magic combination to make it work.

--

Jeff

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[Jeff Ward]

Hey Florian, thanks for the response!

What's in libdart_vm_precompiled_runtime?

Also, is my conclusion about Dart_CreateIsolate no longer supporting NULL vm / isolate snapshots correct?

I did actually made some progress on this last night (by consulting main.cc, I'll outline the fixes at the end for future generations) but still having some issues.

Once I have a hello_world.dart file loaded, I attempt to invoke main using Dart_Invoke, and I'm getting an error message along the lines of "Dart_Invoke expects the library in 'target' to be loaded". I'm not sure what to call to load the "library" other than call Dart_LoadScript (or Dart_LoadLibrary, both do the same thing). I've added a Dart_RunLoop (which main.cc does) but that doesn't seem to fix the issue.

Any thoughts?

How I Fixed My Dumb Issues:

First, I made sure that I'm not doing any extra work fro the vm-service isolate that gets created when you call Dart_Initialize. In the creation callbacks I checked for Dart_IsServiceIssolate and break out if that's the case.

Second, the dart:builtin module is now called dart:_builtin. Loading that library worked.

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[Florian Schneider]

On Tue, Apr 19, 2016 at 5:26 PM, Jeff Ward <je...@fuzzybinary.com> wrote:

Hey Florian, thanks for the response!

What's in libdart_vm_precompiled_runtime?

libdart_vm_precompiled_runtime is used to run programs from a precompiled instruction snapshot - basically a Dart app compiled into a .so file.

 

Also, is my conclusion about Dart_CreateIsolate no longer supporting NULL vm / isolate snapshots correct?

 

Passing NULL is supported. For example, see runtime/bin/gen_snapshot.cc - it loads all sources from source files instead of a snapshot. Maybe gen_snapshot is actually a better (simpler) example to start from than main.cc -- but instead of creating and writing a snapshot you would invoke main there.